1. Field of the Invention
The present invention relates to a heat treatment apparatus for heat-treating a semiconductor wafer or a glass substrate (hereinafter simply referred to as a “substrate”) by means of light irradiation thereon.
2. Description of the Background Art
Conventional ion activation process of a semiconductor wafer after being subjected to ion implantation employs a heat treatment apparatus such as a lamp annealing apparatus using a halogen lamp. In such a heat treatment apparatus, a semiconductor wafer is heated up (annealed) to a temperature of about 1000 to 1100° C. to realize ion activation of the semiconductor wafer. Light energy emitted from the halogen lamp is operative to cause temperature rise of the wafer at a speed of about several hundreds of degrees centigrade per second.
An example of a lamp annealing apparatus using a halogen lamp is introduced in Japanese Patent Application Laid-Open No. 2001-127001, in which a metal surface in a processing chamber is covered with a coating material to suppress diffusion of metallic component from the metal surface during heat treatment.
Even in a heat treatment apparatus which realizes ion activation of a semiconductor wafer by means of temperature rise of the wafer at a speed of about several hundreds of degrees centigrade per second, ions implanted into the semiconductor wafer exhibit a rounded profile, which means ion diffusion by heat. Occurrence of this phenomenon necessitates implantation of ions in a greater amount than necessary, as the surface of the semiconductor wafer subjected to ion implantation with even high concentration experiences diffusion of the implanted ions therefrom.
In response, the surface of a semiconductor wafer is irradiated with flashlight by a xenon flash lamp, for example, so that only the surface of the semiconductor wafer implanted with ions is allowed to rise in temperature in a very short period of time of not longer than several milliseconds. An example of such a technique is introduced in Japanese Patent Application Laid-Open No. 59-169125 (1984) and No. 63-166219 (1988). Temperature rise in a very short period of time by use of a xenon flash lamp does not allow a period long enough for ion diffusion, thereby realizing ion activation with no rounding of a profile of ions implanted into a semiconductor wafer.
In a conventional heat treatment apparatus using a xenon flash lamp, a semiconductor wafer is contained in a stainless steel chamber, and the wafer surface is irradiated with flashlight. At this time, the inner wall of the chamber is also subjected to irradiation with flashlight emitted from the flash lamp.
The light emitted from the xenon flash lamp has considerably high intensity, which may result in generation of a brown oxide film during heat treatment that covers a metal surface inside the chamber. Even a slight source of contamination may result in imperfect treatment in light of recent trends toward high precision of a semiconductor device, for example. Generation of such an oxide film is thus unfavorable.
Necessity to minimize the source of contamination leading to particle contamination or metal contamination is not limited to an apparatus employing heating system by means of light irradiation, but is common to a conventional heat treatment apparatus for a semiconductor device, for example. Japanese Patent Application Laid-Open No. 2002-60926 suggests a cleaning technique responsive thereto, in which a deposited material adhered to a component in a heat treatment chamber, for example, is heated to sublimate. Another cleaning technique includes removal of a product of the decomposition of source gas adhered to a heat treatment chamber by means of heat treatment in an atmosphere such as halogen gas, an example of which is suggested in Japanese Patent Application Laid-Open No. 2002-313727.
In addition to the foregoing adherence of a deposited material, contamination of a heat treatment chamber results from various reasons. By way of example, a semiconductor wafer under treatment may crack, causing a treatment chamber to be littered with the fragments thereof. Especially in a heat treatment apparatus using a xenon flash lamp, a semiconductor wafer is instantaneously irradiated with considerably high-energy light, thereby causing rapid temperature rise of the surface of the semiconductor wafer in a moment. As a result, the semiconductor wafer may crack due to rapid thermal expansion of the surface.
The resultant fragments of the semiconductor wafer cannot be removed by heat treatment, for example. The treatment chamber should be opened for mechanically cleaning the inside. However, a heat treatment chamber with a complicated configuration cannot be easily cleaned, imposing difficulty in completely removing the source of pollution such as fragments of a semiconductor wafer.